U.S. patent number 7,528,676 [Application Number 11/785,228] was granted by the patent office on 2009-05-05 for balun circuit suitable for integration with chip antenna.
This patent grant is currently assigned to TDK Corporation. Invention is credited to Denver Humphrey, Brian Kearns, Joseph Modro.
United States Patent |
7,528,676 |
Kearns , et al. |
May 5, 2009 |
Balun circuit suitable for integration with chip antenna
Abstract
A balun including a single-ended port, a differential port and
first and second sets of coupled transmission line sections. Each
set has three coupled transmission line sections. The signal
carrying terminal of the single-ended port is connected to an inner
end of a third coupled transmission line sections in one of the
sets, and the terminals of the differential port are connected to a
respective outer end of a respective first transmission line. The
balun is fabricated in a multi-layer insulating substrate with the
single-ended port located on an upper surface of the substrate and
the differential port located on a lower surface of the substrate.
The balun is suitable for connection to a chip antenna mounted on a
common carrier substrate.
Inventors: |
Kearns; Brian (Dublin,
IE), Humphrey; Denver (Broughshane, IE),
Modro; Joseph (Dublin, IE) |
Assignee: |
TDK Corporation (Tokyo,
JP)
|
Family
ID: |
39853173 |
Appl.
No.: |
11/785,228 |
Filed: |
April 16, 2007 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20080252393 A1 |
Oct 16, 2008 |
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Current U.S.
Class: |
333/26;
333/185 |
Current CPC
Class: |
H01P
5/10 (20130101) |
Current International
Class: |
H03H
7/42 (20060101); H01P 1/10 (20060101) |
Field of
Search: |
;333/25,26,185 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Gavela I. et al., "A Small Size LTCC Balun for Wireless
Applications," 2004, Proceedings of the European Microwave
Conference, pp. 373-376. cited by other.
|
Primary Examiner: Takaoka; Dean O
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
The invention claimed is:
1. A balun comprising a single-ended port comprising a
signal-carrying terminal; a differential port comprising a first
signal-carrying terminal and a second signal-carrying terminal; and
first and second sets of coupled transmission line sections, said
first and second sets being located adjacent to one another; each
of said first and second sets comprising a respective first
transmission line section and a respective second transmission line
section, each transmission line section within each set having a
respective inner end and a respective outer end, said respective
first transmission line sections being connected together in series
at their respective inner ends, said respective second transmission
line sections being connected together in series at their
respective inner ends, wherein each of said first and second sets
includes a respective third coupled transmission line section
having a respective outer end connected to the respective outer end
of the respective second transmission line section, and wherein
said signal-carrying terminal of said single-ended port is
connected to an inner end of one of said third coupled transmission
line sections, and wherein said first and second signal-carrying
terminals of said differential port are connected to a respective
outer end of said first transmission line sections.
2. A balun as claimed in claim 1, wherein said transmission line
sections of at least one of said first and second sets are coupled
in a broadside manner.
3. A balun as claimed in claim 1, wherein said transmission line
sections of at least one of said first and second-sets are
substantially in register with one another in a direction
transverse of each of said transmission line sections in the
respective set.
4. A balun as claimed in claim 1, wherein a respective shunt
capacitor is connected between said respective outer ends of said
first transmission line sections and electrical ground.
5. A balun as claimed in claim 1, wherein a respective shunt
capacitor is connected between said respective inner ends of said
third transmission line sections and electrical ground.
6. A balun as claimed in claim 1, wherein a respective shunt
capacitor is connected between said respective outer ends of said
third transmission line sections and electrical ground.
7. A balun as claimed in claim 1, wherein a shunt capacitor is
connected between said connected inner ends of said first
transmission line sections and electrical ground.
8. A balun as claimed in claim 1, wherein the combined lengths of
said respective first transmission line sections of said first and
second sets is less than one half of the wavelength of a signal at
a centre frequency of an operating frequency band of said
balun.
9. A balun as claimed in claim 1, wherein the combined lengths of
said respective second transmission line sections of said first and
second sets is less than one half of the wavelength of a signal at
a centre frequency of an operating frequency band of said
balun.
10. A balun as claimed in claim 1, wherein the combined lengths of
said respective third transmission line sections of said first and
second sets is less than one half of the wavelength of a signal at
a centre frequency of an operating frequency band of said
balun.
11. A balun as claimed in claim 1, comprising a multi-layer
insulating substrate in which said first and second sets of coupled
transmission line sections are arranged in a respective stack, said
respective stacks being located adjacent to one another in said
multi-layer insulating substrate.
12. A balun as claimed in claim 11, wherein each transmission line
section within a respective stack is provided on a respective layer
of the multi-layer substrate.
13. A balun as claimed in claim 12, wherein said respective first
transmission line sections are provided on a respective common
substrate layer, said respective second transmission line sections
are provided on a respective common substrate layer, and said
respective third transmission line sections are provided on a
respective common substrate layer.
14. A balun as claimed in claim 13, wherein connections between
adjacent transmission line sections on a respective common
substrate layer are made by arranging said adjacent transmission
line sections to be contiguous.
15. A balun as claimed in claim 11, wherein connections between
transmission line sections in non-common substrate layers are made
by at least one electrically conductive via.
16. A balun as claimed in claim 11, wherein said multi-layer
substrate has an obverse face and a reverse face, said reverse face
being mountable on a support substrate, and wherein said respective
stacks are arranged such that said respective first transmission
line sections are located proximal said obverse face, said
respective third transmission line sections are located proximal
said reverse face and said respective second transmission line
sections are located between said respective first and third
transmission line sections.
17. A balun as claimed in claim 16, wherein said signal-carrying
terminal of said single-ended port is provided at, said obverse
face and said first and second terminals of said differential port
are provided at said reverse face.
18. A balun as claimed in claim 16, wherein said first and second
signal-carrying terminals of said differential port are located at
respective opposite sides of said multi-layer substrate, said
signal-carrying terminal of said single-ended port being located
between said opposite sides.
19. A balun as claimed in claim 18, wherein said signal-carrying
terminal of said single-ended port is located substantially midway
between said opposite sides.
20. A balun as claimed in claim 16, wherein said signal-carrying
terminal of said single-ended port is electrically connected to a
single-ended port of an antenna, wherein said antenna and balun are
mounted adjacent to one another on a support substrate with said
respective single-ended ports being substantially aligned with one
another.
21. A balun as claimed in claim 20, wherein said antenna and said
balun are fabricated in a common multi-layer insulating structure.
Description
FIELD OF THE INVENTION
The present invention relates to baluns. The invention relates
particularly to baluns for use with antennae of wireless
communications devices.
BACKGROUND OF THE INVENTION
Differential circuits have been employed in wireless cellular
communications handsets and other wireless systems for many years.
The principal benefits from using differential circuits as opposed
to single-ended circuits are lower noise and lower susceptibility
to interference. Despite the benefits of differential circuits,
some of the components used in a modern wireless communications
systems remain single-ended. For example, single-ended antennae are
more common than differential antennae. In cases where wireless
communications systems include single-ended and differential
components, it is necessary to include devices which convert the
single-ended signals which are incident on and emitted from the
single-ended components to differential signals which are incident
on and emitted from the differential components. Conversely,
devices which convert the differential signals which are incident
on and emitted from the differential components to single-ended
signals which are incident on and emitted from the single-ended
components are also required.
Such devices are often referred to as baluns. Figures of merit for
describing the electrical characteristics of a balun which converts
a single-ended signal to a differential signal are the single-ended
to differential mode response, the single-ended to common mode
response, the amplitude balance, and the phase balance. Figures of
merit for describing the electrical characteristics of a balun
which converts a differential signal to a single-ended signal are
the differential mode to single-ended response, the common mode to
single-ended response, and the amplitude and phase balance.
A balun can be implemented by a number of discrete components.
Balun topologies employing discrete components are taught in U.S.
Pat. No. 5,949,299 (Harada) and U.S. Pat. No. 6,396,362 (Mourant et
al). Baluns can also be implemented using distributed components,
normally employing pairs of serially connected quarter-wavelength
coupled lines. A popular form of the distributed balun is often
referred to as a Marchand balun. A variation of the Marchand balun
is taught in U.S. patent US06292070 (Merrill) and is commonly
referred to as a backwards-wave balun. Distributed baluns such as
the Marchand balun and the backwards-wave balun typically offer
excellent performance over a wide bandwidth.
FIG. 1 shows the structure of a conventional Marchand balun, the
structure has a first pair of transmission lines 10A, 10B, a second
pair of transmission lines 11A, 11B, a differential port 12 and a
single-ended port 13. The length of each transmission line is
substantially equal to one quarter of the wavelength at the centre
of the operating frequency band of the balun. During use,
electromagnetic coupling occurs between the respective transmission
lines in each pair 10A, 10B and 11A, 11B.
The structure of a backwards-wave balun is depicted in FIG. 2, the
structure has a first pair of transmission lines 20A, 20B, a second
pair of transmission lines 21A, 21B, a differential port 22 and a
single-ended port 23. The length of each transmission line is
substantially equal to one quarter of the wavelength at the centre
of the operating frequency band of the balun. During use,
electromagnetic coupling occurs between the respective transmission
lines in each pair 20A, 20B and 21A, 21B.
FIG. 3 shows a size-reduced Marchand balun as described in Gavela
I., Falagan M. A., Fluhr H.; "A Small Size LTCC Balun for Wireless
Applications"; Proceedings of the European Microwave Conference
2004; pp 373-376. The structure of this balun is similar to that of
FIG. 1 and includes a first pair of transmission lines 30A, 30B, a
second pair of transmission lines 31A, 31B, a differential port 32
and a single-ended port 33. In addition, two shunt capacitors 34A
and 34B are provided, as shown, with the effect that the required
length of each of transmission lines 30A, 30B and 31A, 31B is less
than one quarter of the wavelength at the centre of the operating
frequency band of the balun.
FIG. 4 shows another size-reduced balun as taught in U.S. Pat. No.
6,801,101 (Hiroshima et al); the balun includes a first pair of
transmission lines 40A, 40B, a second pair of transmission lines
41A, 41B, a differential port 42 and a single-ended port 43. The
balun additionally includes shunt capacitors 44A, 44B, 45A, 45B and
46, as shown, an effect of which is that the required length of
each of the transmission lines is less than one quarter of the
wavelength at the centre of the operating frequency band of the
balun.
Where an antenna having a single-ended input/output (I/O) port is
required to be connected to a differential I/O port of a
transceiver, a balun is required. However, connection from the
single-ended I/O port of the antenna to the differential I/O port
of the transceiver is not always readily achievable using
conventional baluns. For example, FIG. 5 shows a chip antenna 50 as
taught in U.S. Pat. No. 7,042,402 (Modro). The chip antenna 50 is
typically mounted on a PCB or substrate 57 so that the main
radiating section is at a raised elevation relative to the surface
of the substrate 57. Consequently, the co-planar single-ended-port
of the antenna, comprising signal-carrying terminal 52 and ground
terminals 53B and 53B, are also at a raised elevation relative to
the surface of the substrate 57. On the other hand, the terminals
(not shown) of the differential port of a transceiver (not shown),
or other transmitter or receiver circuitry, to which the antenna is
to be connected via a balun are normally located on the surface of
the substrate 57.
Unfortunately, none of the conventional balun circuits shown in
FIGS. 1, 3 or 4 can be easily arranged to provide a balun with
signal-carrying terminals appropriately located on upper and lower
faces to allow the antenna 50 to be coupled to a transceiver
because, in each case, the single ended I/O port is located at one
end of the balun structure.
The I/O ports of the backwards wave balun of FIG. 2 are suitably
positioned so that a backwards wave balun could be arranged to
provide signal-carrying terminals located as required on the upper
and lower faces of the balun. However, the requirement for three
direct connections to electrical ground on the single-ended side of
the backwards-wave balun of FIG. 2 represents a significant design
challenge at radio frequencies (RF), because the required elevation
of the signal-carrying terminal of the single-ended port of the
balun, and the required lower location of the terminals of its
differential port dictate that coupled line sections 20A and 21A
should be located towards the lower section of the balun and
coupled line sections 20B and 21B should be located near the upper
section of the balun. Hence, the ground connections would
necessarily be made using long metal filled via holes inside the
balun, but there is an inevitable parasitic inductance associated
with such via holes.
SUMMARY OF THE INVENTION
Accordingly, the invention provides a balun comprising a
single-ended port comprising a signal-carrying terminal; a
differential port comprising a first signal-carrying terminal and a
second signal-carrying terminal; and first and second sets of
coupled transmission line sections, said first and second sets
being located adjacent to one another; each of said first and
second sets comprising a respective first transmission line section
and a respective second transmission line section, each
transmission line section within each set having a respective inner
end and a respective outer end, said respective first transmission
line sections being connected together in series at their
respective inner ends, said respective second transmission line
sections being connected together in series at their respective
inner ends, wherein each of said first and second sets includes a
respective third coupled transmission line section having a
respective outer end connected to the respective outer end of the
respective second transmission line section, and wherein said
signal-carrying terminal of said single-ended port is connected to
an inner end of one of said third coupled transmission line
sections, and wherein said first and second signal-carrying
terminals of said differential port are connected to a respective
outer end of said first transmission line sections.
The balun may be formed within a parallelepiped shaped substrate,
wherein said single-ended I/O port comprises a single
signal-carrying terminal, said differential I/O port comprises a
first and second signal-carrying terminal, wherein said
single-ended port is located on an upper face of said
parallelepiped, wherein said differential port is located on a
lower face of said parallelepiped, wherein said first and second
signal-carrying terminals of said differential port are positioned
approximately symmetrically about an intersecting plane of said
parallelepiped which intersects said lower and said upper face
along medians of said faces and wherein said single signal-carrying
terminal of said single-ended port is positioned so that it is
intersected by said median of said upper face.
Preferably, said first and second sets of coupled transmission line
sections comprise transmission line sections which are broadside
coupled.
Preferably, said first transmission line section of said first set
and said first transmission line section of said second set are
located towards the lower face of said parallelepiped, and said
third transmission line section of said first set and said third
transmission line section of said second set are located towards
the upper face of said parallelepiped.
Preferably, said transmission line sections of said first and
second sets of coupled transmission line sections of said balun are
not connected directly to electrical ground at any point along
their lengths, and moreover, connections to electrical ground are
made via shunt capacitors of said balun.
Further advantageous aspects of the invention will be apparent to
those ordinarily skilled in the art upon review of the following
description of specific embodiments of the invention and with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are now described by way of example
and with reference to the accompanying drawings in which like
numerals are used to indicate like parts and in which:
FIG. 1 shows a prior art Marchand balun;
FIG. 2 shows a prior art a backwards-wave balun;
FIG. 3 shows a prior art size-reduced Marchand balun;
FIG. 4 shows an alternative prior art size-reduced balun;
FIG. 5 shows a known chip antenna with a single-ended I/O port at a
raised elevation relative to a mounting surface of the antenna;
FIG. 6 shows an RF circuit comprising the single-ended antenna of
FIG. 5 and a balun embodying the invention;
FIG. 7 shows a balun circuit suitable for use in the balun of FIG.
6;
FIG. 8 shows an alternative balun circuit suitable for use in the
balun of FIG. 6;
FIG. 9 shows a three dimensional layout of the balun of FIG. 6 when
implemented using the balun circuit of FIG. 8, suitable for
fabrication in a multilayer substrate such as low temperature
co-fired ceramic (LTCC);
FIG. 10A shows the differential mode response and the common mode
response resulting from a circuit simulation of the balun circuit
of FIG. 8; and
FIG. 10B shown the amplitude and phase balance resulting from the
same circuit simulation.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 6 shows an example of an implementation of an RF circuit
comprising the single-ended antenna 60 corresponding to the
single-ended antenna 50 of FIG. 5 and a balun 61 embodying one
aspect of the invention. The balun 61 includes a single-ended port
comprising signal-carrying terminal 64 and a differential port
comprising signal-carrying terminals 65A and 65B where the
terminals of the balun 61 are arranged so that antenna 60 and the
balun 61 are easily aligned and can be mounted on common substrate
67 in a space saving manner. The signal-carrying terminals 65A, 65B
are suitable for connection to corresponding terminals of a
differential port of transceiver circuitry (not shown) or other
circuitry for receiving and/or transmitting signals via the antenna
60. The preferred way to realize balun 61 is as a distributed
circuit comprising coupled line sections fabricated in a
multilayered substrate such as low temperature co-fired ceramic
(LTCC). It is advantageous to use broadside coupled line sections
since they offer the benefit over edge coupled line sections that
the transition from signal-carrying terminals 65A and 65B of the
differential port of the balun 61 to signal-carrying terminal 64 of
the single-ended port of the balun 61 can be achieved using
relatively short metal filled via holes formed within the substrate
of the balun 61.
FIG. 7 shows a balun circuit 78 embodying one aspect of the
invention and suitable for use as the balun 61. The balun 78
comprises a differential I/O port 72 and a single ended I/O port
73, and has a specified operating frequency band over which a
balanced signal incident on the differential port 72 is converted
to an unbalanced signal emitted from the single-ended port 73, and
vice versa. The balun 78 comprises a first set of coupled
transmission line sections 70A, 70B, 70C, and a second set of
coupled transmission line sections 71A, 71B and 71C. Coupled
transmission line sections 70A and 71A are connected in series with
one another and coupled transmission line sections 70B and 71B are
also connected in series with one another. The first and second
sets of transmission line sections are located adjacent to one
another so that each transmission line section of a given set has
an inner end which is proximal or adjacent to the other set, and an
outer end which is distal the other set. The outer ends of coupled
transmission line sections 70A and 71A are connected to a
respective terminal of the differential port 72. The outer ends of
coupled transmission line sections 70B and 71B are connected
respectively to the outer ends of coupled transmission line
sections 70C and 71C. The inner end of coupled transmission line
section 71C is connected to the signal-carrying terminal of the
single-ended port 73.
Preferably, the balun 78 of FIG. 7 includes size-reducing shunt
capacitors 74A and 74B, connected to the respective outer ends of
coupled transmission line sections 70A and 71A. It is also
preferred that the balun 78 includes size-reducing shunt capacitors
75A and 75B, connected to the respective inner ends of coupled
transmission line sections 70C and 71C. The effect of size-reducing
shunt capacitors 74A, 74B, 75A and 75B is that the required
electrical length of each of coupled transmission line sections
70A, 70B, and 70C, and 71A, 71B, and 71C is less than one quarter
of a wavelength at the centre of the operating frequency band of
the balun. In an alternative embodiment (not illustrated), where
shunt capacitors 74A, 74B, 75A, 75B are omitted, the electrical
length of each of coupled transmission line sections 70A, 70B, and
70C, and 71A, 71B, and 71C is substantially equal to one quarter of
a wavelength at the centre of the operating frequency band of the
balun.
Preferably, the balun 78 includes a shunt capacitor 76 connected at
the node where the respective inner ends of coupled transmission
line sections 70A and 71A are connected together. The effect of
shunt capacitor 76 is to improve the ratio of the single-ended to
differential mode response of the balun 78 and the single-ended to
common mode response of the balun 78 over a given frequency range.
Preferably, the frequency range over which the improvement offered
by shunt capacitor 76 coincides with the operating band of the
balun 78. The improvement in the ratio of the single-ended to
differential mode response and the single-ended to common mode
response of the balun 78 arising from shunt capacitor 76 is due to
a reduction in the odd mode impedance between the outer ends of
coupled line sections 70A and 71A.
FIG. 8 shows an alternative embodiment of a balun circuit 88. The
balun 88 comprises a differential I/O port 82 and a single-ended
I/O port 83 and has a specified operating frequency band. The balun
88 comprises a first set of coupled transmission line sections 80A,
80B, 80C, and a second set of coupled transmission line sections
81A, 81B and 81C. Coupled transmission line sections 80A and 81A
are connected in series with one another, and coupled transmission
line sections 80B and 81B are also connected in series with one
another. The outer ends of coupled transmission line sections 80A
and 81A are connected to respective terminals of the differential
port 82. The outer ends of coupled transmission line sections 80B
and 81B are connected respectively to the outer ends of coupled
transmission line sections 80C and 81C. The inner end of coupled
transmission line section 81C is connected to the single-ended port
83. The inner end of coupled transmission line section 80C is left
open circuit.
Preferably, the balun 88 of FIG. 8 includes size-reducing shunt
capacitors 84A and 84B, connected respectively to the outer ends of
coupled transmission line sections 80A and 81A. It is also
preferred that the balun 88 includes size-reducing shunt capacitors
85A and 85B, connected respectively at the nodes where outer ends
of coupled transmission line sections 80B and 80C meet and where
coupled transmission line sections 81B and 81C meet
respectively.
Preferably, the balun 88 includes a shunt capacitor 86 connected at
the node where the respective inner ends of coupled transmission
line sections 80A and 81A are connected together. The effect of
shunt capacitor 86 is to improve the ratio of the single-ended to
differential mode response of the balun 88 and the single-ended to
common mode response of the balun 88 over a given frequency
range.
During use of balun circuits 78, 88, electromagnetic coupling
occurs between the respective transmission line sections of each
set, and in particular, when the balun circuits 78, 88 carry
signals in the respective operating frequency bands. The coupling
of transmission lines may be determined by the proximity of the
transmission lines to one another, by the characteristics of the
substrate in which they are embedded and by the manner in which
they are aligned. Broadside coupling of transmission lines within
each set is preferred, especially wherein each transmission line in
a set is substantially in register with each other transmission
line in the set. Even though the electromagnetic coupling occurs
during use, the transmission lines within each set may be referred
to as coupled transmission lines, since they are arranged such that
coupling occurs during use.
In FIGS. 7 and 8, the respective baluns 78, 88 have three
transmission line sections in each coupled set. In alternative
embodiments (not illustrated), each set of coupled transmission
line sections may include more than three coupled transmission line
sections.
FIG. 9 shows, generally indicated as 98, an example of a three
dimensional implementation of the balun 88, suitable for
fabrication in a multilayer substrate such as low temperature
co-fired ceramic (LTCC). The balun 98 may be fabricated in a
multilayer substrate comprising 6 insulating or dielectric layers,
L1 to L6, with metal patterns on the top of each layer to provide
the balun components. A ground electrode GND and a pair of I/O
electrodes 92A and 92B are disposed on the underside (as viewed in
FIG. 9) of the balun 98 where the I/O electrodes 92A and 92B
correspond to the signal-carrying terminals of the differential
port 82 of FIG. 8. The balun 98 comprises a first set of broadside
coupled transmission line sections 90A, 90B, 90C, and a second set
of broadside coupled transmission line sections 91A, 91B, 91C.
Coupled transmission line sections 90A and 91A are connected in
series with one another and coupled transmission line sections 90B
and 91B are also connected in series with one another. The outer
ends of coupled transmission line sections 90A and 91A are
connected to differential I/O electrodes 92A and 92B respectively
via conducting vias or through holes TH formed in the insulating
substrate. The outer ends of coupled transmission line sections 90B
and 91B are connected to the outer ends of coupled transmission
line sections 90C and 91C respectively by means of electrically
conducting through holes TH. The inner end of coupled transmission
line section 91C is connected to I/O electrode 93 by means of a
pair of through holes TH and a metal trace Ti fabricated on the
upper (as viewed in FIG. 9) surface of dielectric layer L5. I/O
electrode 93 corresponds to the signal-carrying terminal of the
single-ended port 83 of FIG. 8.
The balun 98 further comprises shunt capacitors 94A and 94B
connected to the outer ends of coupled line sections 90A and 91A,
shunt capacitors 95A and 95B connected to the outer ends of coupled
line sections 90C and 91C, and shunt capacitor 96 connected at the
point where coupled line sections 90A and 91A are connected
together.
The balun 98 is mounted on a substrate 97 comprising I/O trace
lines 99A and 99B, which may be connected to the differential I/O
port of a transceiver circuit (not shown) located elsewhere on the
surface of substrate 97. It will be seen that the terminals 92A,
92B of the differential port are located on opposite sides of the
balun 98, while the terminal 93 of the single ended port is located
between and above (with respect to the substrate) the terminals
92A, 92B. In particular, in the illustrated embodiment, the single
ended I/O terminal 93 is located towards, or substantially at, the
centre of one of the sides of the top surface of the balun 98.
Hence, the balun 98 is suitable for connection to, for example, the
chip antenna 50 of FIG. 5, and as shown in FIG. 6.
FIG. 10A shows the differential mode response and the common mode
response resulting from a circuit simulation of the balun of FIG.
8, where the physical dimensions of the coupled line sections 80A,
80B, 80C and 81A, 81B, 81C and the capacitors 84A, 84B and 85A, 85B
are chosen to provide a balun with an operating band from 3.168 to
4.752 GHz which coincides with band group I of the Ultra Wide Band
system as defined by the WiMedia Alliance.
It can be seen that the insertion loss of a differential signal is
marginally higher than 0.5 dB across the band, and that the
attenuation of common mode signal is 20 dB or greater across the
band. Both of these results are acceptable considering the
bandwidth.
FIG. 10B shown the amplitude and phase balance of the balun of FIG.
8. It can be seen that amplitude balance is better than +/-1 dB
across the operating band, and the phase balance is better than
+/-10 degrees across the operating band of the balun.
In the preferred embodiment, the first and second sets of coupled
transmission line sections are not connected directly to electrical
ground at any point along the lengths of the constituent
transmission line sections of said coupled transmission line
sections. Moreover, connections to electrical ground from said
coupled transmission line sections are advantageously made via
shunt capacitors.
In preferred embodiments, the combined length of the respective
first, second or third transmission line section of the first set
of coupled transmission line sections and the corresponding first
second or third transmission line section of the second set of
coupled transmission line sections is less than one half of the
wavelength of a signal at the centre of the operating frequency
band of the balun. In alternative embodiments, where size reducing
capacitors are not used, the combined length of the respective
first, second or third transmission line section of the first set
of coupled transmission line sections and the corresponding first
second or third transmission line section of the second set of
coupled transmission line sections is preferably substantially
equal to one half of the wavelength of a signal at the centre of
said operating frequency band of the balun
The balun is usually mounted on a carrier substrate and may be
positioned adjacent to an antenna mounted on the same carrier
substrate, wherein electrical connection is made from the
single-ended I/O port of the balun to the antenna by an electrical
connector.
The antenna is advantageously fabricated within the same substrate
as the balun. The combination of the balun and antenna within a
single substrate ostensibly providing a balanced feed antenna.
The invention is not limited to the embodiments described herein
which may be modified or varied without departing from the scope of
the invention.
* * * * *